12-Bit To 24-Bit Registered Bus Exchanger With 3-State Outputs
This 12-bit to 24-bit registered Bus Exchanger is designed for 1.65-V to 3.6-V VCC operation.
The SN74ALVCH162268 is used for applications in which data must be transferred from a narrow high-speed bus to a wide, lower-frequency bus.
The device provides synchronous data exchange between the two ports. Data is stored in the internal Registers on the low-to-high transition of the Clock (CLK) input when the appropriate clock-enable (CLKEN) inputs are low. The select (SEL) line is synchronous with CLK and selects 1B or 2B input data for the A outputs.
For data transfer in the A-to-B direction, a two-stage pipeline is provided in the A-to-1B path, with a single storage Register in the A-to-2B path. Proper control of these inputs allows two sequential 12-bit words to be presented synchronously as a 24-bit word on the B port. Data flow is controlled by the active-low output enables (OEA, OEB). These control terminals are registered, so bus direction changes are synchronous with CLK.
The B outputs, which are designed to sink up to 12 mA, include equivalent 26- resistors to reduce overshoot and undershoot.
To ensure the high-impedance state during power up or power down, a Clock pulse should be applied as soon as possible and OE should be tied to VCC through a pullup resistor; the minimum value of the resistor is determined by the current-sinking capability of the driver. Due to OE being routed through a Register the active state of the outputs cannot be determined prior to the arrival of the first Clock pulse.
Active bus-hold circuitry holds unused or undriven inputs at a valid Logic state. Use of pullup or pulldown resistors with the bus-hold circuitry is not recommended.
By Texas Instruments
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